The fungicidal activity of human salivary histidine-rich polypeptides on candida albicans

Abstract

The purpose of this investigation was to determine the fungicidal effects of human parotid salivary histidine rich-polypeptides (HRP) on Candida albicans. Three strains of Candida albicans were used in the current investigation. Two of the three strains were isolated from patients at Boston University Hospital. The third strain was Candida albicans B311. Human parotid saliva was collected from healthy donors using the method described by Curby ( 1953). The parotid saliva was lyophilized and subsequently stored at -20 degree C. After chromatography procedures, parotid saliva protein was separated into 2 fractions. Peak 1(HRP 1) and Peak 2 (HRP II). Peak 1 contained the bulk of salivary proteins whereas Peak 2 was found to be enriched with basic histidine-rich polypeptides. Other protein samples such as egg white lysozyme and synthetic homopolymers (poly-L-histidine, poly-L-arginine and poly-L-lysine) were also tested to compare their effects with those of salivary protein fractions. Assays were designed to determine protein effects on: 1 ) killing of Candida albicans yeast form, 2) killing of Candida albicans hypha form and 3) inhibition of yeast to mycelium transformation (germination ) of Candida albicans. The results showed that HRP II protein samples (enriched with basic histidine-rich polypeptides) had a potent killing effect on both yeast and hypha form organisms. HRP 1, which contained the bulk of salivarγ proteins, did not affect the viability of the yeast or hypha form organisms. These results were statistically significant (pく0.0005 at 20([mega]g/ml) suggesting that histidine-rich polypeptides exert antifungal effects in vivo, Inhibition of yeast to mycelium transformation of Candida albicans was not affected by HRP1 or by HRP II. The lack of inhibition of Candida albicans germination by both HRP 1 and HRP II salivary fractions could possibly be attributed to: l ) the experimental conditions were not appropriate or 2) the HRP fractious did not have the ability to inhibit germination of Candida albicans. The killing effects of yeast and hypha fungi forms and the inhibition of yeast to mycelium transformation by synthetic polypeptides and egg white lysozyme were also tested. Poly-L-histidine and poly-L-lysine showed killing activity against yeast and hypha fungi forms of Candida albicans.These synthetic polypeptides also significantly inhibited the yeast to mycelium transformation of the organism. Lysozyme did not affect the viability of yeast and hypha for organisms or inhibit the yeast to mycelium transformation of Candida albicans.